A. Field of the Invention
This invention relates generally to the treatment, extraction, and detoxification of contaminated mixed solid wastes including soils, sludges, and contaminated debris that contain hazardous and radioactive contaminants. The treatment of these contaminated streams has become a national environmental priority, since such streams are being created by so many sources such as landfills, surface impoundments, research, industry, power plants, government and many other chemical, pharmaceutical, biological, electroplating, photographic processes and waste generators.
More specifically this invention involves a novel process that extracts and concentrates contaminates from solid waste materials and catalytically oxidizes volatile pollutants, all of which are contained in the mixed wastes that can be treated by this invention. The novel process disclosed herein couples an extraction system for dissolution of the contaminants, a solid/liquid separation system coupled with efficient evaporation and gas phase catalytic oxidation. Optionally, this process can provide for the recapture of soil or debris that is substantially free of the contaminants and that may, therefore, be safely returned to the site or the removal area.
B. Description of Prior Processes
The treatment and purification of solid waste materials contaminated with hazardous and radioactive compounds has long been a problem because of the difficulties associated with removing these types of contaminants from the solids. More often than not solid wastes contain volatile and nonvolatile components that, if not properly treated, would cause massive pollution of the environment.
The art has recognized a number of processes for treating various types of wastes, several of which involve evaporation steps to concentrate the solids phase prior to further treatment of the concentrated solids. Treatment of harmful volatile components prior to introduction in the environment is also known to the art. An oxidation process is the most typical of treatment processes for volatilized contaminants.
Likewise, the art describes many extraction processes, including soil washing and solvent extraction processes. Each of these processes use a variety of combined equipment. Mixing tanks and other solids/liquid contacting devices are known. A particular liquid/solid contactor is a waste pulper, known as a Hydrapulper, manufactured by Black Clawson located at Middletown, Ohio which has been used for many years in the paper industry to defiber wood pulp. It has been used for tar sand processing. Hydrapulper literature from Black Clawson indicates that the apparatus may be used in applications besides pulping. Possible applications disclosed include chemicals, rendering and agricultural residues.
U.S. Pat. No. 4,005,480 (Smith, et al.) describes the use of a waste pulper similar to those used in the lumber industry to reduce the size of tar sand pieces. U.S. Pat. No. 3,788,568 (Marsh) describes the use of a waste pulper to grind municipal wastes for classification purposes.
Evaporation processes for treating polluted waste streams are well known to the art. In particular vertical tube falling film evaporation with vapor recompression has been suggested to efficiently concentrate wastewater streams containing a high concentration of total dissolved solids. The use of such evaporators is described in an ASME publication entitled "Development History of the RCC Brine Concentrator For Concentrating Cooling Tower Blow Down", by J.H. Anderson, 1976.
Distillation of water and catalytic oxidation of residues in sewage and other contaminated liquids by contacting the wet waste with a molten salt is disclosed in U.S. Pat. No. 3,642,582 (Greenberg et al.). The molten salt provides two functions. The first is a heat transfer medium to effect evaporation of the water in the waste and the second is to catalyze the oxidation of organic residue remaining after evaporation. Likewise, in U.S. Pat. No. 3,688,120 (Patterson) molten metal is used to convert human organic waste into harmless gases. A bath of molten lead, maintained at 620.degree. F. to 900.degree. F., is the preferred metal to effect evaporation of water and oxidation of organic compounds in the waste stream.
In general, oxidation of organic compounds dissolved in wastewater streams is well known in the art. Both liquid phase and vapor phase oxidation processes are known. For example, industrial fluids, such as dyestuff solutions, can be purified using the process disclosed in U.S. Pat. No. 4,279,693 (Kuhnlein et al.). This process involves evaporation of impurities from polluted fluids where approximately 90% of the volatile impurities remain untreated or are subjected to flame combustion at temperatures ranging from 800.degree.-1000.degree. C. A small percentage of the impurities (approximately 10%) may be removed from the nonvolatiles and destroyed in a catalytic oxidation process. The catalytic oxidation process operates in a nonstream environment with a low water-to-organic ratio. U.S. Pat. No. 4,141,829 (Thiel et al). discloses a two step oxidation process. In the first step a contaminated water stream is subjected to a liquid oxidation process to destory the majority of the organic substances in the liquid stream. Any volatile organics remaining after the liquid oxidation step are heated and catalytically oxidized in a gas phase reactor. U.S Pat. No. 4,021,500 (Rogers) discloses an improved oxidative dehydration system to catalytically remove dissolved hydrocarbons. A hydrocarbon laden liquid water stream is mixed with an air/steam stream and is contacted with a solid catalyst to yield an effluent of water vapor, carbon monoxide and carbon dioxide.
U.S. Pat. No. 4,699,720 (Harada et al.) teaches a process for treating wastewater wherein a stream containing suspended solids, ammonia and chemically oxidizable substances is subjected to a liquid phase catalytic oxidation reaction. Separation of the suspended or dissolved solids occurs after the oxidation reaction by employing a reverse osmosis process. Likewise, U.S. Pat. No. 4,632,766 (Firnhaber et al.) discloses a method of treating wastewater wherein a concentrated "slime" containing water is subjected to a noncatalytic multistage oxidation in the presence of air or oxygen. Yet another wastewater treatment process using liquid phase catalytic oxidation is disclosed in U.S. Pat. No. 4,294,706 (Kakihara et al.). This reference suggests the removal of suspended solids prior to treatment (Column 3, lines 12-15).
Extraction of volatile contaminates from waste streams followed by catalytic destruction of the volatized contaminates has been practiced in the art. For example, U.S. Pat. No. 3,127,243 (Konikoff) teaches a process whereby human waste is subjected to a noncontinuous vacuum distillation process to produce vaporized materials that are passed to a high temperature catalytic reactor containing a noble metal catalyst. The reaction product is then condensed to produce potable water. Likewise, U.S. Pat. No. 3,487,016 (Zeff) teaches the oxidation of organic or inorganic materials in liquid or vapor phase using oxygen-containing gas and a catalyst containing either manganese or lead. Oxidation is performed at low temperatures and at atmospheric or less pressure. U.S. Pat. No. 3,804,756 (Callahan et al.) teaches that volatile impurities may be steam stripped from wastewaters and then chemically oxidized with a variety of catalyst formulations, with copper oxide being preferred.
The elimination of volatile organic compounds (VOC) from industrial/commercial waste gases is also well known in the art. Destruction of VOC is accomplished by catalytic incinerators. An article entitled, "Destruction of Volatile Organic Compounds Via Catalytic Incineration" authored by B. H. Tichenor and M. A. Palazzol, Environmental Progress, Volume 6, No. 3, August, 1987, reports the results of an investigation into various catalytic incinerator designs. Tests were performed by evaporating organic compounds into clean air streams and then passing the streams across a monolithically supported precious metal catalyst. Catalytic incineration of noxious industrial fumes is also disclosed in U.S. Pat. No. 4,330,513 (Hunter et al.). This reference discloses a process where fumes and waste gases containing hydrocarbons are contacted with a fluidized bed of nonprecious metal solid catalyst. Additionally, a series of U.S. Pat. Nos. 3,823,088; 3,992,295; 3,997,440; 4,062,772; 4,072,608 and 4,268,399 teach that waters containing minor amounts of dissolved organic materials can be purified by contacting either a liquid or gaseous phase with a promoted zinc albuminate catalyst.
Although the art has understood the need and has attempted the treatment of waste streams and contaminated gas streams, it has failed to solve the problem of efficiently treating mixed waste streams contaminated with volatile organics, toxic metals and radioactive contaminants. The present invention presents a novel continuous treatment method for extracting radioactive contaminants, concentrating those contaminants to a liquid phase, dewatering the treated solids, concentrating the nonvolatile components and chemically oxidizing volatile contaminants. Further, this invention presents a combination of extraction, and concentration in essentially a closed system whereby a small amount of extractant solution (blowdown) containing the contaminants and water are further treated by evaporation and catalytic oxidation.